The present invention concerns heparin derivatives, processes for their preparation, pharmaceutical substances containing these heparin derivatives and their use in the treatment of disturbances in fat metabolism.
Sulfated glycosamino glycan heparin has long been in use a postoperative, subcutaneous thrombo-embollic prophylactic agent at low doses of 3.times.5,000 IU daily, but in relatively larger doses for the treatment of extracorporeal circulations for the prevention of blood coagulation when used in connection with, for example, blood oxygenation, surgery with the use of the heart-lung machine, hemodialysis, hemofiltration, hemoperfusion and plasmaphoresis. Even as part of the heparin therapy after thrombo-embolic conditions, i.e., venous thrombosis or pulmonary embolism, heparin salts are administered in intravenous doses of 30,000 to 40,000 IU/24 hours.
In such cases, heparin is known to have an inhibitory effect on the coagulation system by potentiating the action of the plasmatic inhibitor antithrombin III with regard to the coagulation factors Xa and thrombin. Independent of its influence on the coagulation system, it also acts in fat metabolism by induction of the release of the so-called clearing factor, a lipoprotein lipase bound to the vessels. The latter effect predestines heparin for the treatment of hyperlipidemia, for which it is administered preferably in low doses over a relatively long time.
A danger of hyperlipidemia is that in the plasma, lipids are not present in a free state but are conjugated with each other and with carrier proteins. Abnormal accumulation of lipoproteins (e.g., containing cholesterol), particularly low density lipoproteins, is associated with the development of atherosclerosis. See Robins and Angell, Basic Pathology, pages 271-74, 2nd Ed. (1976).
To decrease the associated effect of an increase in the coagulation time, which is dangerous for the patient, attempts were made to modify heparin chemically in such a way that, while still retaining its lipid-lowering action, it loses its anticoagulant potency which is expressed, for example, in its ability to inhibit coagulation in the blood plasma. Thus, the decoupling of lipid-lowering and coagulation-inhibiting action has been the subject of numerous publications. For example, the problem of whether low molecular weight heparin fractions or heparin fragments with a decreased anticoagulant action can be used therapeutically for the elevation of the lipoprotein lipase level is being studied intensively at present (K. Etienne et al., Br. J. Clin. Pharmac. 16: 712-714, 1983).
The chemical structure of heparin as well as some structural prerequisites for its action have been almost completely established. Thus it is known that the action of heparin on the fat metabolism is facilitated mainly by its O-sulfate groups (sulfuric acid ester groups) while the anticoagulant activity is correlated with the content of N-sulfate groups such as sulfamine groups. (K. Andrassy, "Nierenund Hochdruckkrankheiten," 10 (No. 3): 96, 1981). As is known by one skilled in the art, the anticoagulant effect as well as the effect of heparin on the so-called clearing factor declines during the course of acid hydrolysis of heparin with mineral acids, where the acid-labile, N-sulfate groups are cleaved more readily than the O-sulfate groups. Also known is the fact that both of the therapeutic effects of heparin discussed herein (mobilization of lipoprotein lipase and anticoagulant potency) are lowered or completely lost during the course of continued hydrolysis. For example, B. Casu et al. report in Arzneimittel -Forschung/Drug Res. 33(I): No. 1, 1983 a correlation between the fat-clearing activity and the behavior of SO.sub.3.sup.- /COO.sup.- -groups in heparins and heparin sulfates.
U.S. Pat. No. 3,118,816 describes N-succinyl derivatives of heparin that can potentiate the activity of lipoprotein lipase in warm-blood animals without any apparent influence on the blood coagulation times. Such derivatives are prepared by refluxing heparin with aqueous 0.09 N HCl and then reacting with succinyl chloride to form N-succinyl heparin, in which between 25% and 35% of the glucosamine-N-atoms have been succinylated. The product has a coagulation activity of 7 USP units/mg.
A considerably more drastic hydrolysis method for heparin is disclosed in German Offenlegensschrift DE-OS No. 31 23 806, wherein heparins of different origins are subjected to a hydrolysis with 0.33N mineral acids, e.g. hydrochloric acid, at 100.degree. for 6 hours, which hydrolyze the acid-labile sulfamine groups completely and the acid-stable O-sulfate groups partially. A subsequent succinylation with succinic anhydride results in a product with a coagulation activity below 0.05 USP units/mg.
Because of the extremely drastic hydrolysis conditions or due to the conditions of the derivation reaction, the polyanionic structural characteristics of the succinylated heparin derivatives contribute to an increase in the lipid-lowering effect in contrast to pure, underivatized hydrolyzates, but only about half of the lipid-lowering activity of the heparin used in the reaction is obtained. Moreover, the foregoing studies, without exception, have as their objective the indirect therapeutic lowering of the lipid level in the blood by the use of the modified heparins, i.e. by elevation of the enzyme activity of a lipoprotein lipase (clearing factor).
German Offenlegensschrift DE-OS No. 31 35 814 discloses the selective precipitation of low-density lipoproteins (LDL) or beta-lipoproteins from whole serum or plasma with the aid of heparin at acid pH values with the consequent direct and specific reduction of the content of this risk factor in the blood. The disadvantage of this method, however, is the lasting risk to the patient due to the strong anticoagulant effect induced by the relatively high heparin level required for the therapeutic treatment.
Thus, there remains a need for a heparin derivative that causes the precipitation of low-density lipoproteins while minimizing or eliminating the anticoagulent effect thereof.